In known embodiments of semiconductor rectifying systems, particularly those having high reverse voltage handling capability, and which include at least one semiconductor body, the semiconductor body is customarily completely encased in an insulating material. The insulating material may be either a molded or cast mass, and consists of at least one organic base material, preferably a resin, together with fillers, such as, for example, quartz flour or aluminum oxide, primarily to improve the thermal operating characteristics of the material.
The surface of the semiconductor body not intended to be contacted is thus specially provided with a protective coating in the vicinity of the outlet of the p-n junction, said coating consisting, for example, of the oxide of the semiconductor material, or of a protective lacquer made from organic vehicles and special additives. This coating is intended to offset the harmful influence of undesirable impurities in the form of atoms, ions or molecules disposed on the semiconductor surface or in the surrounding atmosphere, on the biasing ability of such semiconductor devices.
The insulating material required after making such insulating and/or stabilizing coatings in order to encapsulate the semiconductor body is specifically determined, with reference to its composition and properties, by the requirements placed on housings for semiconductor devices.
In connection with the requirement for more and more economical embodiments of semiconductor rectifier systems, the use of insulating materials serving to encapsulate semiconductor bodies and simultaneously suited to protect the semiconductor surface in order to optimize the blocking behavior, result in a significant economic advantage since special process steps for the so-called surface stabilization are eliminated.
The problem of producing encapsulation masses having stabilizing properties has been described in German Auslegeschrift (Published Patent Application) No. 1,903,098. This publication discloses an electrically insulating epoxy resin encapsulation material for semiconductor devices which material consists of an unhardened epoxy resin, an amine, phenol or anhydride hardener, an additive in the form of an organic silicon compound, i.e. a lower alkyl, alkoxy silane, having a low degree of polymerization and, if required, an inorganic filler, and is also intended to effect a passivating surface treatment of the semiconductor devices.
It has been found, however, that such known, so-called silanized insulating materials produce the desired surface stabilization only for transistors, but for semiconductor devices having a reverse voltage carrying capability higher by one or two orders of magnitudes than that of transistors they can no longer effect such stabilization.
It is therefore the object of the present invention to produce insulating materials for encapsulating semiconductor bodies for rectifier systems having a high reverse voltage carrying capability and for protecting the semiconductor surface against undesirable impurities.